1. Field of the Invention
This invention relates to a filtration system for airborne particles. More particularly, the present invention relates to a filtration enhancement apparatus which promotes particle conglomeration and increased filtration efficiency.
2. Description of the Background Art
Increasing indoor air quality has become critically important in recent decades. One reason for this is that since the mid-1970s, HVAC systems are using less outside air within buildings in an effort to reduce energy consumption. As a result there is more air recirculation within buildings and a need to more effectively remove contaminants from such air. Airborne contaminants can be either aerosols or gases. Aerosols are composed of either solid or liquid particles, whereas gases are molecules that are neither liquid nor solid and expand indefinitely to fill the surrounding space. Both types of contaminants exist at the micron and submicron level.
Most dust particles, for example, are between 5-10 microns in size (a micron is approximately 1/25,400th of an inch). Other airborne contaminants can be much smaller. Cigarette smoke consists of gases and particles up to 4 microns in size. Bacteria and viruses are another example of airborne contaminants. Bacteria commonly range anywhere between 0.3 to 2 microns in size. Viruses can be as small as 0.05 microns in size.
The importance of removing these contaminants varies based upon the application. Semiconductor clean rooms and hospital operating rooms are two examples of spaces where the ability to remove contaminants is critical. One factor complicating the removal of contaminants is that particle density increases with smaller particle size. For example, in the typical cubic foot of outside air there are approximately 1000 10-30 micron sized particles. The same volume of air, however, contains well over one million 0.5 to 1.0 micron particles. Ultimately, 98.4949% of all airborne particles are less then a micron in size.
The prevalence of small particles is problematic from an air quality perspective because small particles are harder to control. This is because the dominating transport mechanism for particles smaller than a couple of microns in diameter is not airflow but electromagnetic forces. All building environments have complex electrical fields that interact with smaller particles. These interactions determine the deposition of contaminants in and on people, objects, ductwork, furniture and walls. Among the sources of these fields are electrical lines, in-wall cables, fluorescent lights and computers. Because most particles are less than one micron in size, most particles are dominantly influenced by these fields.
For the fewer, larger particles, airflow is the dominant transport mechanism. These particles travel through a room unaffected by the surrounding electromagnetic fields. These larger particles are typically larger than 2-3 microns in size and have less free charge associated with them. In most rooms, these particles are transported by HVAC equipment. Because these larger airborne particles make up only 1% of the contamination in the average building, traditional HVAC equipment cannot be relied upon for decontamination. Thus, there exists a need in the art to effectively eliminate contaminants that are made up of smaller particles. The following references illustrate the state of the art in air purification systems.
U.S. Pat. No. 5,061,296 to Sengpiel et al. discloses an air purification system that subjects air to a complex electric field including sensors and a monitor/controller for monitoring the effectiveness and operational conditions of an electrical field, as well as the ambient conditions of the air being purified.
Similarly, U.S. Pat. Nos. 5,401,299 and 5,542,964 to Kroeger et. al. disclose an air purification apparatus where air is subjected to a complex electric field resulting from a DC voltage and an AC frequency in the kilovolt and kilohertz range respectively. The DC voltage and AC frequency are applied to a screen assembly in the path of the air.
Although the above referenced inventions achieve their own individual objectives, they do not disclose a filtration enhancement system whereby smaller particles are effectively eliminated via particle conglomeration.